I. Field of the Invention
The present invention relates to data communication. More particularly, the present invention relates to a novel and improved data buffer structures for storing symbols received for multiple physical and transport channels in a CDMA system.
II. Description of the Related Art
A modern day communication system is required to support a variety of applications. One such communication system is a code division multiple access (CDMA) system that supports voice and data communication between users over a terrestrial link. The use of CDMA techniques in a multiple access communication system is disclosed in U.S. Pat. No. 4,901,307, entitled “SPREAD SPECTRUM MULTIPLE ACCESS COMMUNICATION SYSTEM USING SATELLITE OR TERRESTRIAL REPEATERS,” and U.S. Pat. No. 5,103,459, entitled “SYSTEM AND METHOD FOR GENERATING WAVEFORMS IN A CDMA CELLULAR TELEPHONE SYSTEM,” both assigned to the assignee of the present invention and incorporated herein by reference.
A CDMA system is typically designed to conform to one or more standards. One such first generation standard is the “TIA/EIA/IS-95 Terminal-Base Station Compatibility Standard for Dual-Mode Wideband Spread Spectrum Cellular System,” hereinafter referred to as the IS-95 standard and incorporated herein by reference. The IS-95 CDMA systems are able to transmit voice data and (albeit not efficiently) packet data. A newer generation standard that can more efficiently transmit packet data is offered by a consortium named “3rd Generation Partnership Project” (3GPP) and embodied in a set of documents including Document Nos. 3G TS 25.211, 3G TS 25.212, 3G TS 25.213, 3G TS 25.214, and 3G TR 25.926, which are readily available to the public. The 3GPP standard is hereinafter referred to as the W-CDMA standard and incorporated herein by reference.
The W-CDMA standard defines a channel structure capable of supporting a number of users and designed for efficient transmission of packet data. In accordance with the W-CDMA standard, data to be transmitted is processed as one or more “transport” channels at a higher signaling layer. The transport channels support concurrent transmission of different types of services (e.g., voice, video, data, and so on). The transport channels are then mapped to one or more “physical” channels that are assigned to a user terminal for a communication (e.g., a call).
The W-CDMA standard allows for a great deal of flexibility in the processing of the transport channels. For example, data for a particular transport channel can be coded using a convolutional code, a Turbo code, or not coded at all. Also, the data can be interleaved over one of four different time intervals (i.e., 10 msec, 20 msec, 40 msec, or 80 msec) to provide temporal diversity against deleterious path effects (e.g., fading, multipaths, and so on). Different combinations of coding scheme and interleaving interval can be selected to provide improved performance for different types of services. For example, enhanced efficiency and performance may be obtained by processing packet data using Turbo code and a long interleaving interval, which may result in longer processing delays. In contrast, voice and video data may be processed using convolutional code and a short interleaving interval since long processing delays cannot be tolerated.
A user terminal in a W-CDMA system may receive multiple transmissions (i.e., multiple transport channels) concurrently via multiple physical channels. For costs consideration, it is highly desirable to design a user terminal capable of processing multiple physical and transport channels using a basic set of processing and storage elements. In particular, data buffer structures that can be used to efficiently store data received for multiple physical/transport channels, and to facilitate the processing of such data, are highly desirable.